The standardization of the LTE (Long Term Evolution) system, which is the 3.9th generation wireless communication system for mobile phones, has been substantially completed. Recently, the standardization of LTE-A (LTE-Advanced, also called IMT-A), which is a development of the LTE system and is a candidate for the 4th generation wireless communication system, has been progressing.
In uplink (communication from a mobile station to a base station) in the LTE system, DFT-S-OFDM (Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing, also called SC-FDMA), in which spectra are allocated to contiguous frequency bands so as to have a good PAPR (Peak to Average Power Ratio) characteristic, is employed. Regarding the LTE-A system, a decision has been made to employ, in addition to DFT-S-OFDM, clustered DFT-S-OFDM (also called DSC (Dynamic Spectrum Control) or DFT-S-OFDM with SDC (Spectrum Division Control)), in which clusters generated by dividing a signal spectrum are allocated to non-contiguous frequency bands.
Furthermore, a decision has been made to increase the bandwidth to obtain a higher peak data rate, and also a decision has been made to use a system band used in the LTE system as a component carrier (CC, also called a Primary Component Carrier or Secondary Component Carrier) and perform carrier aggregation (CA) for simultaneous transmission on a plurality of CCs. For data transmission in an uplink using CA, N-times DFT-S-OFDM is employed. N-times DFT-S-OFDM is multi-carrier transmission in which frequency signals generated through DFT are assigned to respective CCs.
In clustered DFT-S-OFDM employed as an uplink transmission method for LTE-A, spectra are non-contiguously allocated within one CC and frequencies with a good channel are used, so that a frequency selection diversity gain is obtained. Accordingly, frequency utilization efficiency increases. On the other hand, in N-times DFT-S-OFDM, simultaneous transmission is performed using a plurality of CCs, in which spectra are allocated to non-contiguous frequency bands. Thus, broadband transmission can be realized, and a higher peak data rate can be obtained.
However, there is a problem with data transmission using such non-contiguous frequency bands in that a large amount of spurious emission is generated, particularly in a case where spectra are allocated to distant frequency bands (see NPL 1). An uplink in the LTE system is based on the assumption that data transmission is performed using a continuous frequency band, and thus transmit power control (TPC) is optimized for transmission using a continuous frequency band. The problem of spurious emission arises as a result of applying the method of transmit power control to clustered DFT-S-OFDM or N-times DFT-S-OFDM. Regarding TPC, methods suitable for data transmission using non-contiguous frequency bands are being studied. An example of the methods is a method for changing MPR (Maximum Power Reduction) in accordance with the spacing of frequencies when signals are allocated in the case of using non-contiguous frequency bands (see NPL 2).